1. Field of the Invention
This invention relates to an expandable polyetherimide composition. More particularly, it relates to an expandable composition which gives a useful polyetherimide foam which is excellent in heat resistance and non-flammability, does not emit harmful smoke and flames even in a fire, and is useful as a heat insulating material and a shock absorbing material, and to a foamed material obtained therefrom.
2. Description of the Prior Art
As to heat insulating materials and shock absorbing materials excellent in heat resistance, there have been hitherto known foamed materials of various heat resistant polymers, for example that of poly(2,6-dimethylphenylen oxide) (U.S. Pat. No. 3,492,249) and those of polysulfone, polyarylsulfone and polyethersulfone [Japanese Patent Application Kokoku (Past-Exam Publn) No. 36004/83]. However, these heat resistant resins are essentially non-inflammable and moreover emit a large amount of smoke in a fire. Accordingly, they cannot be used as interior finish materials of aeroplanes, vehicles and motorcars.
Besides the above-mentioned foamed materials, there have been also proposed polyimide foam [Japanese Patent Application Kokai (Laid Open) No. 145222/84] and heat resistant foamed materials formed of resins having a glass transition point of 140.degree. C. or higher [Japanese Patent Application Kokai (Laid Open) No. 36139/84]. However, though the former is excellent in heat resistance and substantially emits no harmful smoke and flame, it has drawbacks in that it requires the use of expensive raw materials and moreover gives final products of high moisture absorption. On the other hand, the latter has defects in that it has a open cell content resulting in a poor heat insulating property, and moreover has poor mechanical strength and shock absorbing property. Thus, they are both not satisfactory as heat resistant foamed material.